Garvan Walshe was National and International Security Adviser to the Conservative Party until 2008.

The Ghost of Niccolò Machiavelli appeared me last night here in Florence. He dictated to me this letter to the heads of government at the NATO Summit.

Dear Sirs and Madams,

You find yourselves assembled in a town called Newport, when your alliance is facing its stiffest challenge since the end of the Cold War. Quite why you chose this particular town is beyond me. Had you wanted to be far away from Russia (a difficult proposition given the size of that country), would it not have been better to choose Porto or Santiago de Compostela, where the weather is quite nice at this time of year? Never mind: your internal customs are not my affair, and it is better you stick to them than ruffle feathers by altering them for no obvious purpose.

In my Florence we had a collective leadership rather like yours, the Signoria, presided over by a primus inter pares, whom we gave the wonderful tittle of Gonfalionere di Giustizia, and you seem to call President of the United States. In theory they were all equal members, but in practice they were connected by power and family loyalty (I see that one of you is even a Florentine, but I’m not sure I trust him). Rich families like the Medici would, through careful use of their money (for theirs was never so great as to overwhelm the other families) suborn the official processes of our republic, which is why we drove them out, and why, when they managed to buy and bully their way back, our republican institutions were destroyed. I will have more to say on the corrupting power of money presently. It is highly relevant to your fate.

Your enemy is that new prince of Russia, Vladimir Putin. He fancies himself a man who possesses in abundance the quality I call virtù — do not confuse it with your virtue; it’s more like what you call “balls” admixed with wisdom — and which any new leader needs to refound his state. He does not lack it entirely. He has at least given some basic order back to Russia. Pensions are paid on time. Magnates have become rich; but he had the sense to take them down when they began to have designs on the Kremlin of their very own.

But he is too fond of the theatrical gesture to properly live up to the standards he has set himself: why did he release Khodorkovsky, if it was not part of a process of putting relations with Europe back on an even keel? That might have made sense, if he had also decided to abandon Yanukovich, and gain for Russia legitimacy in the international system. Nor has he pursued his war with the required vigour. Why are the soldiers he got killed in Ukraine buried in secret, with their wives and mothers not knowing where they are rather than celebrated at least as patriotic “volunteers”? Is it because he hasn’t prepared his people for his planned aggression. Then he would have done better to have prepared them properly, or resigned himself to the loss of influence in Ukraine provoked by the incompetence of his client there. This tells me that Putin lacks the constancy to pick a policy and stick to it with the required thoroughness. He thinks he can achieve his aims without paying the price. In this, men and women of the signoria, you have your opportunity.

But you must display resolve and unity. The fabric of your constitution; what with your long-winded modern words you call the “rules-based international architecture” is at risk. Those rules, which allow you to expend very few resources keep your State at peace (I hear most of you don’t even spend one fiftieth of your country’s resources on you army) only hold when everyone else thinks they will too. Keep up your defences now, so you won’t have to take emergency measures to shore them up later.

As with Florence, the love of money has led several of you, who should be its leading members, astray. Mr Cameron – the main Russian families, who stole their wealth from the Russian people, use your country as a bank. Can you not at least use your laws to deprive them of these stolen goods? Mrs Merkel – the more your merchants do business with Moscow, the more it clouds your administration’s judgement. It may cost a little now to toughen up; Russia is like a usurious money-lender, the price it exacts only ever goes up. If your Social Democrat allies were really worried worried about the people’s welfare, they would reduce their taxes, not put the security of the state at risk. And Mr Hollande, you showed a spark of virtù last week when you purged the Count of Montebourg from your council. Now do the same, and cancel that warship.

The love of money corrupts a city and is the beginning of its downfall. It requires “wise balls” to resist it. Show Mr Putin that you have them.